In recent years, study systems are being developed which present a question, receive an answer input by a user, and present a correctness evaluation. In a study system, it is necessary to precisely infer the degree of understanding of the user during the study, in order to improve the efficiency of studying. The reason is that, if the degree of understanding of the user can be precisely inferred, it becomes possible to present a question in accordance with the degree of understanding and appropriately adjust content to be fed back as to what sort of content should be output with respect to an answer.
In such a study system, the degree of confidence as to how confident a user was in making his or her answer is a piece of information which is important in inferring the degree of understanding of the user. Various techniques for measuring the degree of confidence have conventionally been studied.
For example, Patent Document 1 discloses a study system which, when a condition such as a question level is input, automatically selects an exercise. This study system measures the degree of confidence of a user by collecting a subjective evaluation of the user for each question, in the form of a questionnaire, during study. Then, based on the degree of confidence and the correctness of the answer, the study system infers the degree of understanding of the user, and selects and asks exercises in accordance with the degree of understanding of the user.
Patent Document 2 discloses a technique of inferring a user state based on biological information. In Patent Document 2, a user state when a difference has occurred between a user's anticipation of an appliance operation and an actual appliance operation is defined as a disappointment. Then, the appliance detects a disappointment state of the user, by using a disappointment signal component (positive component) which appears in an event-related potential as an index. A disappointment signal component appears in the case where, with respect to a confident manipulation, an appliance has failed to operate as expected. Thus, by using this signal it is possible to measure the degree of confidence with respect to a manipulation. Utilizing the characteristics of an event-related potential, this appliance detects a disappointment state of a user immediately (about 600 ms) after an answer input, and thus realizes a change of an interactive service.    [Patent Document 1] Pamphlet of International Laid-Open No. WO2003/050782    [Patent Document 2] Pamphlet of International Laid-Open No. WO2005/001677